The conversations are furious and exasperated: "When will it end?" "How is he leading?" "What do we do about him?"

These are the sounds in campaign headquarters of candidates not named Trump. In these offices, solving for the Donald has become a major distraction and disruption.

Who are his supporters? Understanding the Trump voter is tricky, mostly because Trump is a relatively new phenomenon in presidential politics, and without a political record it's difficult to measure where his support is coming from.

But I'm pretty sure I know where it's not coming from: the conservative base.

Today's prototypical conservative base voters are infamously principled. Their views are hardened, their heels dug in. They are armed with all kinds of litmus tests and purity tests to make sure the "fake" conservatives are weeded out from the good ones, often to the chagrin of the party.

It shifts with time, but at the moment the ideological guillotine falls on issues like immigration (are you for a pathway?), abortion (are you for exceptions?), guns (are you for universal background checks?), education (do you support Common Core?) and climate change (do you think it's real?). Departing from doctrine on just one of these can cast a foreboding shadow of skepticism upon an otherwise devout and disciplined conservative.

For Republican base voters, Chris Christie and Jeb Bush are unforgivably moderate. While to the rest of the country people like John McCain and Mitt Romney are sufficiently conservative if not "severely" conservative, to use Romney's phrasing, to the hardened base voter the 2008 and 2012 presidential losses were proof that voting for the so-called "electable" candidate, instead of the principled one, leaves them with nothing to show for it. They got neither the satisfaction of voting their conscience -- be it for Ron Paul, Mike Huckabee or Rick Santorum -- nor the consolation of a less than conservative Republican in the White House.

The idea that in 2016 these voters would simply turn off their hardwired orthodoxy and support a guy who has voted for Democrats, said "the economy does better under the Democrats," refused to pledge to support the Republican nominee if it's not him, openly defended Planned Parenthood, approved of exceptions to abortion bans, supported a single-payer healthcare system, backed an assault weapons ban and advocated a one-time 14.25 percent mega-tax on the wealthy to erase the national debt is, to put it in Trumpian language, really, really stupid.

Base voters will stick with candidates like Rand Paul and Ted Cruz, who demonstrated their conservative bona fides by shutting down the government, filibustering the Patriot Act and pledging to repeal Obamacare. The more evangelically inclined will support Huckabee and Santorum, or maybe even Marco Rubio, who recently said he personally opposes any exceptions -- rape, incest, health of the mother -- for abortion.

So who is the Trump supporter, if not the conservative base? I'd argue it's mostly disaffected moderates who no longer strictly identify with either party. They think the political system is rigged. They think politicians are corrupt. They want a total collapse of the ruling political class.

While Trump probably gets more support from the right, running as a Republican, he attracts from the left as well.

Two of his most ardent supporters, a pair of African-American sisters from North Carolina named Lynette Hardaway and Rochelle Richardson are leading a "Stump for Trump" movement and appeared on CNN to talk him up. According to their website, they are Democrats.

A popular Reddit thread that's generated nearly 13,000 comments so far asked Trump supporters to explain why they liked him. A surprising number of Democrats weighed in, including one who said:

"I support Bernie Sanders, but if he doesn't make it past the primaries, then Trump it is. Trump is the only other who isn't bought."

So what does this mean for the other GOP candidates? A serious gamble. If they think there are enough base voters left, they can ignore Trump and hope to be the choice of the serious conservative. But if the base is shrinking -- and it may be -- they'll have to make a play for the disaffected middle. Which means running a primary more like a general election. Yikes.